Technical Field
This invention relates to a self-acting non-return valve which has particular, but not exclusive, application as a replacement heart valve.
A self-acting non-return valve is described in U.K. Patent Specification Nos. 1327371 and 1447871 and has become known as the `Edinburgh valve`. An `Edinburgh valve` employs an aerofoil flap member pivoted in a smooth-bored passage and arranged, under the influence of a fluid flow in one direction through the passage, to turn into an open position in which the valve is substantially aligned with the flow, and on reversal of the flow direction, to turn back through substantially 90.degree. to substantially fully close the passage. The mass distribution of the flap member of an `Edinburgh valve` is normally substantially balanced about the pivoting axis thereof with the aerofoil shaping facilitating lift of the flap member into its open position once flow past the flap member has occurred due to a small fluid pressure differential being generated across the flap member.
Heretofore, the entire area of the flap member of an `Edinburgh valve` has been employed to provide the required aerofoil shape and this, together with the requirement that the transverse cross-section of the flap member at the location of the pivoting axis must be adequate to accommodate the pivot means, has set limits on the design of the flap member so that the pressure drop occurring across the flap member in its open position has consistently been higher than would otherwise be desirable.